1. Field of the Invention
The present invention relates to an apparatus for aiming a pulsed laser beam at a distant target/obstacle in space to ascertain the range thereof, but more specifically, it relates to a laser beam deviation apparatus that uses multifaceted polygonal mirror, inter alia, to aim substantially 100% of the pulsed laser beam at the distant target/obstacle.
2. Description of the Prior Art
In the prior art, a need has been established for aiming a pulsed laser beam at a distant target/obstacle in space whose coordinates are specified only as some elevational angle above the horizon and some azimuthal angle between 0.degree. and 360.degree.. The elevational angle total deviation should be plus or minus 3.degree. about a 0.degree. deviation. The pulsed laser beam should be aimed at the distant target/obstacle in space in a time period not to exceed 300 microseconds.
Present laser beam deviator systems suffer from several deficiencies. Usually, the mirror scanner part of the system is limited to a set up time in the millisecond range. This is orders of magnitude greater than the desired 300 microseconds set up time previously mentioned. Additionally, in the case of acousto-optic type beam deflector systems, the maximum beam throughput available is only 20% to 50% of the energy.
Consequently, there is a need in the prior art for a laser beam deviation apparatus that will set up in 300 microseconds or less while providing substantially 100% of the pulsed laser beam fixed energy for aiming at the target/obstacle.
As background material, U.S. Pat. No. 4,205,348, filed Jul. 5, 1978, to DeBenedictis et al, entitled, "Laser Scanning Utilizing Facet Tracking and Acousto Pulse Imaging Techniques", disclose an apparatus for increasing the efficiency and resolution of a laser scanning system which uses, inter alia, a multifaceted polygonal mirror as a scanner to scan a laser beam across the surface of a recording medium. An acousto-optic Bragg cell is used to deflect the incident laser beam so as to follow one scanner facet of the multifaceted polygonal mirror during a complete scan and shift to the next facet for the following scan.
In DeBenedictis et al, the multifaceted polygonal mirror deflects the laser beam in one dimension only. The polygonal mirror in actuality is a single line scan type deflector and is used to provide angular deflection, i.e., angle multiplier. The acousto-optic (Bragg cell) beam type deflector is used to deflect and/or modulate the incident laser beam, i.e., move the laser beam but not turn it on and off. Accordingly, it is used to keep the incident laser beam in alignment with the polygonal mirror. The loss of throughput in a Bragg cell is unavoidable since whenever the laser beam is bent passing through the device a power loss is certain. This is so because the portion of the beam not deflected is equal to the loss in power of throughput. This amounts to a power loss of 50 to 80% as previously mentioned. The system of DeBenedictis et al will not function as intended without the use of the acousto-optic device described since it is necessary to move the laser beam rapidly across the medium. Thus, the "increase of efficiency" referred to is really an increase in scanning speed due to the use of the Bragg cell while the power efficiency is actually sacrificed, as previously mentioned.
Consequently, there is a need in the prior art to eliminate acousto-optic type devices from laser beam deviation apparatus and to use only a polygonal mirror to deflect the laser beam in two dimensions thereby increasing the system efficiency to substantially 100%.
The prior art, as indicated hereinabove, include many advances in laser beam deviation devices, including increases in scanning speeds. However, insofar as can be determined, no prior art beam deviation device incorporates all of the features and advantages of the present invention.